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Commit 6065fd0d authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: evaluate packet losses upon RTT change 



RACK skips an ACK unless it advances the most recently delivered
TX timestamp (rack.mstamp). Since RACK also uses the most recent
RTT to decide if a packet is lost, RACK should still run the
loss detection whenever the most recent RTT changes. For example,
an ACK that does not advance the timestamp but triggers the cwnd
undo due to reordering, would then use the most recent (higher)
RTT measurement to detect further losses.

Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Reviewed-by: default avatarNeal Cardwell <ncardwell@google.com>
Reviewed-by: default avatarPriyaranjan Jha <priyarjha@google.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 428aec5e

net/ipv4/tcp_recovery.c

+8 −11
Original line number Diff line number Diff line
@@ -117,13 +117,8 @@ void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, 
{

	u32 rtt_us;



	if (tp->rack.mstamp &&

	    !tcp_rack_sent_after(xmit_time, tp->rack.mstamp,

				 end_seq, tp->rack.end_seq))

		return;



	rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time);

	if (sacked & TCPCB_RETRANS) {

	if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) {

		/* If the sacked packet was retransmitted, it's ambiguous

		 * whether the retransmission or the original (or the prior

		 * retransmission) was sacked.
@@ -134,13 +129,15 @@ void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, 
		 * so it's at least one RTT (i.e., retransmission is at least

		 * an RTT later).

		 */

		if (rtt_us < tcp_min_rtt(tp))

		return;

	}

	tp->rack.advanced = 1;

	tp->rack.rtt_us = rtt_us;

	if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp,

				end_seq, tp->rack.end_seq)) {

		tp->rack.mstamp = xmit_time;

		tp->rack.end_seq = end_seq;

	tp->rack.advanced = 1;

	}

}



/* We have waited long enough to accommodate reordering. Mark the expired